Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation with a shaped charge perforating apparatus, as an example.
After drilling the various sections of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation.
Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the desired formation. Specifically, one or more charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or the like. Once the charge carriers are properly positioned in the wellbore such that the shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, the shaped charges create jets that blast through scallops or recesses in the carrier. Each jet creates a hydraulic opening through the casing and the cement and enters the formation forming a perforation.
It has been found, however, that it is sometimes desirable to perforate a wellbore in a particular direction or range of directions relative to the wellbore. For example, in a deviated, inclined or horizontal well, it is frequently beneficial to form perforations in the upward direction, the downward direction or both. Attempts have been made to achieve this goal of perforating wells in particular directions. One method of orienting perforating charges downhole requires the charges to be rigidly mounted in a gun carrier so that they are pointed in the desired directions relative to the carrier. The gun carrier is then conveyed into a wellbore and either laterally biased physically to one side of the wellbore so that the gun carrier seeks the lower portion of the wellbore due to gravity, or the gun carrier is rotatably supported with its center of gravity laterally offset relative to the wellbore. This method relies on the gun carrier rotating in the wellbore, so that the gun carrier may be oriented relative to the force of gravity. Frequently, such orienting rotation is unreliable due to friction between the gun carrier and the wellbore, debris in the wellbore or the like.
More recently, the assignee of the present invention has developed a perforating gun that includes a tubular gun carrier, multiple perforating charges, multiple charge mounting structures and multiple rotating supports. This internally oriented perforating apparatus has successfully provided increased reliability in orienting perforating charges to shoot in the desired directions in a well. In this design, the direction or directions of the perforations is established when the gun is assembly in its manufacturing facility. It has been found, however, that in certain installations, it is necessary to avoid shooting in a particular direction or directions. For example, one or more communication conduits or controls lines may extend along the exterior of the casing string. During installation, these conduits commonly become wound around the casing string such that the exact location of these lines can only determined after installation by, for example, logging the well.
A need has therefore arisen for an apparatus and method operable to achieve reliable downhole orientation of the shaped charges in a perforating apparatus such that the shaped charges shoot in desired directions. In addition, a need has arisen for such an apparatus and method operable to achieve reliable downhole orientation of the shaped charges in a perforating apparatus such that the shaped charges do not shoot in undesired directions.